https://phys.org/news/2018-07-reserve-defense-kinds.html

The plant needs to respond differently depending on the type of threat. Initially, the plant is not able to discern whether the damage to the cell wall is being caused by drought or a disease, for example. So how can plants identify the danger and provide the right response?

Associate Professor Thorsten Hamann at NTNU has been central to finding the answer to this question. "Drought requires a plant to adjust its metabolism, whereas disease requires the plant to activate various immune responses," explains Hamann. Different chemical processes are involved depending on the threat. Physical damage to the cell wall demands a completely different immune solution than disease does.